Method and device for detecting the temperature to which a solid, a liquid or a gas may have been subjected

ABSTRACT

The device comprises a transparent tube (1) wherein may slide freely a part (4) at the extremities of which are arranged two small magnetic masses (5,6). The tube (1), closed at both ends, forms a sealed tank wherein there is placed a phase changing material (7) which is either in a liquid state or in a solid state, according to the temperature to which it has been brought. At one of the ends of the tube (1) a cap (12) containing a removable magnet (9a) is fitted. A fixed magnet (11) is placed at the other end of the tube (1). The part (4) being initially placed on the side of the cap (12), the material (7) is solidified and the removable magnet (9a) is then removed. In the case of exceeding the melting temperature of the material (7), the part (4) attracted by the magnet (11) moves towards the corresponding end of the tube (1), thus making visible a colored ring (14).

BACKGROUND OF THE INVENTION

Means exist for detecting the thermal level to which materials have beensubjected. Detectors are known whose functioning is based for example onthe variation in fluidity of a coloured matter, of which the progressionby capillarity in a support gives a visual indication of exceeding agiven temperature. Detectors using a different principle are also known,where an enzymatic reaction is translated by the variation in colorationof a surface of which the extent also indicates exceeding a thermalthreshold. Such detectors are generally placed in the immediateproximity of the material to be monitored or thereon.

Such detectors present drawbacks: they are expensive, which does notallow use thereof for verifying the freshness of a food product, forexample presented in the form of individual portions. Furthermore, thesedetectors, applied on a product, always indicate the exceeding of asuperficial temperature or one in the proximity. In addition, they areof a certain fragility and cannot without drawbacks be immersed in aliquid or be subjected to compressions or inevitable shocks in thehandling and transport operations. Furthermore, their structure does notallow them to be driven into the material or product to be monitored.

The evolution of eating habits of populations living in so-calleddeveloped countries is more and more oriented towards prepared dishes,cooked in vacuo for example. The life duration of such foodstuffs is afunction of several parameters of which the most important appears to bethe temperature which, when it lies below a determined maximum value,limits proliferation of bacteria. The same applies to the preservation,with maintenance of innocuosness, of certain drugs, including vaccinesand sera. The examples of application set forth hereinabove are notlimiting.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatusfor detecting a rise in temperature to which a material (solid, liquidor gaseous) has been subjected, wherein there is applied to a piecemobile in an at least partially transparent tube a force of displacementtowards a final position which tends to cause the mobile piece to leavean initial position where it is immobilized by a meltable substanceplaced inside the tube, which, on melting when the temperature risessufficiently, releases the mobile piece.

In order to overcome these problems, the invention has a further objectto improve the process of the type described above, so that it makes itpossible to produce devices for detecting a rise in temperature which,although simple and inexpensive, are efficient and offer considerablereliability.

According to the process and above-described object of the invention,the force of displacement applied to the mobile piece is of purelymagnetic origin and is produced by the interaction of magnetic elementscomprising at least one permanent magnet and mounted respectively on thetube and on the mobile piece.

According to another feature of this process, the mobile piece ispreviously brought into initial position by application to this piece ofan arming force likewise of purely magnetic origin, the meltablematerial having been temporarily liquefied to allow this prioroperation.

In general, each of the forces of displacement and of arming employed iseither a force of magnetic attraction or a force of magnetic repulsion.

The method according to the invention is based on the combination of twosimple physical phenomena:

The first phemomenon is, the existence of materials meltable at diversetemperatures which, in the solid state, may prohibit the displacement ofa mobile piece located therewithin and subjected to a force, thisdisplacement becoming possible when the material takes the liquid state,the change of phase being effected at the melting temperature which is acharacteristic constant of the material used;

The second phenomenon relates to the properties of the magneticelements, thanks to which it is possible to apply forces withoutphysical contact, through the solid, liquid or gaseous matters, theseforces, which forces have an origin in magnetic fields issuing frompermanent magnets, being forces of attraction or of repulsion which maybe used separately or in additive or subtractive combination. Theexclusive use of magnetic forces makes it possible to do without anyelastic elements such as springs, whose mechanical properties change asa function of the temperature, with the result that the process offersperfect efficiency and excellent precision both at very high and verylow temperatures.

The present invention also has for an object a device for detecting riseof the temperature of an object, based on the method defined hereinaboveand comprising an oblong piece, mobile in an at least partiallytransparent tube, this piece being subjected to a force which tends tocause it to pass from an initial position, where it is immobilized by ameltable material placed inside the tube, to a final position, themobile piece moving towards this latter position when it is released bythe melting of said material.

According to the invention, the mobile piece comprises, at at least oneof its ends, a magnetic element able to interact with a removablemagnetic element which may be mounted at at least one end of the tube orbe removed therefrom, so as to cause to appear, by positioning,withdrawal or permutation thereof, successively, the arming force ininitial position and the force of displacement towards the finalposition, whilst means are provided for locating the position where themobile piece is located.

Such a detector device employs jointly the change of state of a meltablematter contained in a tubular reservoir, in which is placed a mobilepiece subjected to one or more forces of magnetic origin (attractionand/or repulsion). The positioning or withdrawal of the removablemagnetic elements makes it possible to cause a magnetic force to appearor disappear, whilst its permutation makes it possible, when thiselement is a magnet or anisotropic magnetic element, to reverse thedirection of an existing magnetic force.

Various embodiments of such a device can be envisaged.

The magnetic element of the mobile piece may be a permanent magnet, theremovable magnetic element likewise being a permanent magnet which,depending on the orientation given thereto, exerts a force of attractionor a force of repulsion on the magnetic element of the mobile piece.

The mobile piece may comprise a magnetic element at each of its ends, onwhich may be exerted, by the removable magnetic element, a force in onedirection or in the opposite direction depending on whether this lattermagnetic element is placed at one or at the other of the ends of thetube.

At one end of the tube may be placed a fixed magnetic element, whilstthe mobile piece comprises a magnetic element at each of its ends, theone which faces the fixed magnetic element being respectively eitherrepelled or attracted by the latter, and a removable magnetic element isprovided which may be placed at the other end of the tube, in that caseexerting on the magnetic element of the mobile piece which faces it, aforce respectively either of repulsion greater than the preceding forceof repulsion, or of attraction.

In general, the magnetic elements between which appears a force ofattraction are constituted either by two permanent magnets offering,opposite, poles of opposite signs, or by a permanent magnet and a softiron mass.

Furthermore, when the mobile piece comprises a magnetic element at eachof its ends, these two elements may advantageously be joined to formone, constituted, depending on the case, by a bar of soft iron or anoblong permanent magnet.

For certain particular applications, the tube should be provided with aterminal point making it possible to prick and partially insert thedevice into the object or the matter of which a rise in temperature mustbe detected, so as to allow monitoring of the temperature at the heartof the object or the product into which the device is inserted.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear moreclearly from the following description, with reference to theaccompanying drawings, of non-limiting embodiments.

FIG. 1 shows, in longitudinal half-section, a detector device accordingto the invention which is armed either by turning a magnetic cap or bypositioning the latter at the other end of the device.

FIGS. 2 and 3 similarly show two variant embodiments of a detectordevice according to the invention, provided with a penetration point,which is armed by withdrawal of a magnetic element.

FIG. 4 similarly shows a part of a detector device arranged to indicatethe duration of exceeding of a given temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The different detectors shown employ the change of state of a mattercontained in a reservoir in which is placed a mobile piece subjected toa force of attraction or of repulsion of magnetic origin.

The detector of FIG. 1 is composed of a transparent tube 1 obturated atits two ends by pieces 2 and 3. Inside tube 1 may freely slide, over acertain length l, a piece 4 constituted by a tube, at each of the endsof which has been fitted and immobilized an anisotropic magnetic mass(or magnet) 5, 6. The mobile piece 4 presents a coloured ring 14 orseveral rings coloured alternately with a different colour, thiscoloration advantageously being fluorescent or luminescent.

The tube 1 forms a tight reservoir in which has been introduced, beforeobturation of one of the ends, a phase change material (PCM) 7, whichfills it completely and which is selected so that its physicalcharacteristics of modification of structure, and in particular thetemperature at which from the solid state it becomes liquid again, areperfectly known and immovable. This material may either be synthetic orof animal or vegetable origin; it may also be metallic. It is necessaryand it suffices that its temperature of solidification or ofliquefaction be invariable, liquefaction being equally well pure, as inthe case of water, or an intermediate, so-called "pasty" phase may beadmitted, as in the case of fats for example.

The prototypes made used, as material 7, hexadecene, which is an organicparaffin of which the temperature of change of phase is 2° C. Thedifferent components of said prototypes were made of polycarbonatethermoplastics material for the tubes, the magnetic masses wereelastomers mixed with oriented ferrite powders. Obturation of thetransparent tube 1 forming reservoir was ensured by simple adhesion ofpieces 2 and 3.

Each end of tube 1 may be capped with a removable cap 8 containing amagnet 9. The polarities of the magnets 5 and 9 with respect to eachother are chosen so that, during solidification of the phase changematerial 7, the inner piece 4 is repelled by the action of the magneticfield issuing from the magnet 9 of the cap 8 on the magnet 5, thepolarity of the two opposite magnetic masses being of the same sign. Toput the system into operation, it is necessary and it suffices, thephase change material 7 being in the solid state, to turn through 180°the cap 8 whose magnet 9, in that case presenting a reverse polarity,attracts the inner piece 4 by its magnet 5. It should be noted that suchoperation will be ensured and will produce the same effects if the cap 8is placed at the other end of the tube 1, the direction of fit of thecap being chosen so that the magnetic mass of the magnet 9 that itcontains is of the same polarity as the magnetic mass of the magnet 5opposite it and located at the end of the piece 4.

Under these conditions, the detector being placed either in theenvironment or on the product to be monitored, the translation of thepiece 4 will be produced as soon as the material 7 passes from the solidstate to the liquid state, such displacement being materialized by thedisplacement of the coloured ring 14 of the inner piece 4 with respectto an opaque ring 15 which the outer tube 1 comprises and whichinitially concealed the ring 14.

The variant shown in FIG. 2 demonstrates the exceeding of a temperaturewithin a product or a material by penetration of the detector therein.The present device, of which operation employs phenomena similar tothose which were explained with regard to the device of FIG. 1,comprises: a piece 10 comprising on the one hand a point 10a forpenetration and, on the other hand, a flange 13 limiting penetration ofthe detector. The piece 10 hermetically obturates one end of thetransparent tube 1. Inside this tube and at this same end has beenfitted and immobilized a magnet 11 presenting a magnetic mass of thesame polarity as the magnetic mass of the magnet 6 opposite it. At theother end of the tube 1 is placed a magnet 9 mounted in a removable cap8a and presenting a magnetic mass of the same polarity as the magneticmass of the magnet 5 opposite it and located on piece 4. The variousmagnetic elements are provided so that the intensity of the magneticflux of the magnet 9 is clearly greater than the intensity of the fluxcreated by magnet 11. Consequently, the resultant of the twocorresponding opposite forces causes the repulsion of the inner tube 4towards the penetration point 10a. This initial position of the piece 4being selected for the phase of solidification of the material 7, theremoval of the cap 8a will put the system into operation by creating theapplication to the piece 4 of a force of opposite direction resultingfrom the sole repellant action of the fixed magnet 11 on the magnet 6 ofsaid piece. When the temperature increases to such a point that thephase change material 7 passes into the liquid state again, suchliquefaction causes the displacement of the piece 4 subjected to saidforce, demonstrated by a coloured sector 14 of the piece 4 which thenpresents itself in front of the transparent end of the tube 1 oppositethe point 10a of piece 10.

FIG. 3 illustrates an embodiment which employs only magnetic forces ofattraction. The general structure of this detector is similar to that ofthe detector shown in FIG. 2. A penetration piece 10 terminating in apoint 10a hermetically obturates one of the ends of a transparent tube 1and covers more than half of the length of this tube. The other end ofthe latter is obturated by a fixed cap 12 which caps it over a shortlength d and presents on its terminal face a cavity in which may beinserted, with slight tightening, a magnet 9a in the form of a pellet.At the opposite end of the tube 1 is placed a fixed magnet 11. This tubecontains a tubular inner piece 4 which may move longitudinally thereinover a length l, within a substance 7 capable of passing from the solidstate to the liquid state or vice versa at a determined temperature. Themobile piece 4 comprises at its ends magnets 5, 6. The direction ofmagnetization of the four magnets 9a, 5, 6, 11, merges with the generalaxis 18 of the detector. Moreover, the opposite poles of the adjacentmagnets 6, 11 are of opposite signs. The piece 4 comprises a colouredring 14 which is concealed by the cap 8a made of opaque matter, when themobile piece 4 is in its initial position in the tube 1 (which is thatshown in FIG. 3), whilst this ring becomes visible through that portionof the transparent tube 1 included between the cap 8a and the flange 13of the piece 10 when the piece 4 takes its final position after havingmoved from its initial position towards the point 10a of the piece 10.

Previously, the piece 4 is placed in its initial position, where it isretained by the magnet 9a inserted in the outer cavity of the cap 8a ina direction such that the opposite poles of the magnets 9a and 5 are ofopposite signs, with the result that magnet 9a attracts to it piece 4.

To use the device, it suffices to withdraw the magnet 9a after thesubstance 7 has solidified due to a sufficient drop in temperature. Thepiece 4, consequently subjected to the sole attraction of magnet 11 onits magnet 6, takes its final position as soon as the temperature risesso as to cause the substance 7 to reliquefy. This displacement of piece4 is manifested by the appearance of its coloured ring 14, which ceasesto be concealed by the cap 8a and becomes visible through the wall ofthe tube 1.

It will be noted that, once the tube 4 has thus taken its finalposition, where its magnet 6 adheres to magnet 11 of tube 1, it is nolonger possible (unless extraordinary means are employed) to cause thepiece 4 to return into its initial position. In this way, detection ofthe rise in temperature is effected thanks to an irreversiblephenomenon.

Several variants of the device of FIG. 3 may be envisaged:

Each of the couples 9a, 5 and 6, 11 of magnetic elements may beconstituted, not by two magnets, but by a magnet and a small mass ofsoft iron, the mode of operation of the device remaining unchanged;

The two magnetic elements of the piece 4 may be joined to form one soleelement, viz., depending on the case, a single magnet of oblong form ora piece of rod of soft iron.

A detector according to the invention may be arranged to indicate invisible manner the time during which it was subjected to a temperaturegreater than the point of liquefaction of the meltable material. To thisend (FIG. 4), the mobile piece 4 is perfectly adjusted inside the tube 1and forms therewith a piston-cylinder assembly. The magnetic forces ofdisplacement of the mobile piece 4, acting on the magnet 5 and/or themagnet 6 with which said piece is provided at its ends, cause it to move(towards the left in FIG. 4), the material 7 in the liquid statetransferring from the left end towards the right end of said piece via acalibrated capillary channel 16 pierced axially therein. In this case,the mobile piece 4 is made of a solid transparent bar. The calibratedchannel 16 allows passage only of a well-defined volume, per unit oftime, of the material 7 for a viscosity of determined value thereof,with the result that the length of filling of the channel 16 by thematerial 7, for which care has been taken to colour it, indicates,opposite a graduation scale 17 borne by the transparent tube 1, the timeduring which the temperature at which the detector was exposed exceededthe point of liquefaction of the material 7.

We claim:
 1. A device for detecting a rise in the temperature of anobject or material comprising:a tube that is at least partiallytransparent; a movable piece mounted for movement within the tube; meansfor indicating the position of the movable piece with respect to thetube; a meltable material disposed within the tube and comprising meansfor immobilizing the movable piece in an initial position; and magneticmeans for selectively subjecting the movable piece to a first forceurging the movable piece toward the initial position and a second forceurging the movable piece toward a final position, the movable piecebeing so mounted that melting of the meltable material permits themovable piece to respond to the magnetic means and move toward the finalposition, the magnetic means comprising at least: a first magneticelement; removable mounting means for removably mounting the firstmagnetic element on at least a first end of the tube; and a secondmagnetic element disposed at a first end of the movable piece and beingadapted to interact magnetically with the first magnetic element.
 2. Theapparatus of claim 1, the first and second magnetic elements comprisingpermanent magnets, wherein the removable mounting means comprises meansfor selectively mounting the first magnetic element to selectively exerta force of attraction and a force of repulsion on the second magneticelement.
 3. The apparatus of claim 1, comprising a third magneticelement disposed at a second end of the movable piece, the firstmagnetic element comprising means for interacting with the second andthird magnetic elements to selectively exert thereon a first force inone direction and a second force in an opposite direction when the firstmagnetic element is selectively placed at the first or a second end ofthe tube.
 4. The apparatus of claim 1, comprising a third magneticelement disposed at a second end of the movable piece and a fourthmagnetic element fixed at a second end of the tube in opposition to thethird magnetic element, the third and fourth magnetic elementsexhibiting mutual magnetic repulsion, and wherein, when the removablemounting means is in place on the first end of the tube, the first andsecond magnetic elements exhibit mutual magnetic repulsion that isgreater than the mutual magnetic repulsion between the third and fourthmagnetic elements.
 5. The apparatus of claim 1, comprising a thirdmagnetic element disposed at a second end of the movable piece and afourth magnetic element fixed at a second end of the tube in oppositionto the third magnetic element, the third and fourth magnetic elementsexhibiting mutual magnetic attraction, the first and second magneticelements exhibiting mutual magnetic attraction when the removablemounting means is in place on the first end of the tube.
 6. Theapparatus of one of claims 1-5, comprising at least two magneticallyinteracting permanent magnets having opposed poles of opposite sign. 7.The apparatus of one of claims 1-5, comprising at least two magneticallyinteracting magnetic elements in the form of a permanent magnet and amass of soft iron.
 8. The apparatus of one of claims 1-5, wherein themovable piece comprises a bar of soft iron forming magnetic elements atopposite ends of the movable piece.
 9. The apparatus of one of claims1-5, wherein the movable piece comprises an oblong permanent magnetforming magnetic elements at opposite ends of the movable piece.
 10. Theapparatus of one of claims 1-5, wherein the movable piece comprises abar of transparent matter dimensioned to slide in the tube and having alongitudinal capillary channel formed therein, the capillary channel andthe meltable material being so disposed that movement of the movablepiece upon melting of the meltable material is accompanied by movementof the melted material in the capillary channel, the melted materialhaving a color visible through the movable piece so as to exhibit alength therein that is a function of the duration of time during whichthe apparatus has been exposed to a temperature greater than the meltingpoint of the meltable material.
 11. The apparatus of one of claims 1-5,wherein at least a portion of the external surface of the apparatustapers toward a point for facilitating the pricking of, and insertion ofthe apparatus into, an object or material of which a rise in temperatureis to be detected.